The primary power requirement of an aircraft is for thrust which is provided from its main engine or engines. In a large proportion of aircraft the main engine or engines are gas turbine engines. These conventionally also provide the majority of the secondary power of the aircraft which typically includes hydraulic power to move control surfaces and landing gear, electrical power for control systems, lighting and the like and compressed air power to provide environmental control within the aircraft. Typically the secondary power requirements are derived by mechanical transmission from the aircraft engine or engines which transmission drives one or more electric generators, hydraulic pumps and compressors.
Provision of secondary aircraft power by electrical means has the potential to improve efficiency, reliability and maintainability of aircraft, but requires the use of high power electronic devices, the temperature of which requires to be controlled to ensure satisfactory operation and long life. It has previously been proposed to effect cooling of power electronics by attaching the electronic devices to water cooled aluminium heat sinks. However these are both bulky and relatively heavy and not therefore satisfactory for aero engine applications where weight and volume require to be minimised.
In a wider context, the cooling of electronic or other components is often required in situations where the cooling capacity of an available heat sink may vary over time due to external factors. It may in some circumstances be possible to increase the maximum heat absorbing capacity of the heat sink, but that would inevitably result in increased size and cost and provide over capacity in all but the maximum condition. In other cases it may for various reasons not be possible to increase the capacity of an available heat sink.